Cross-resistance following artificial selection for increased defense against parasitoids in Drosophila melanogaster

An increase in resistance to one natural enemy may result in no correlated change, a positive correlated change, or a negative correlated change in th e ability of the host or prey to resist other natural enemies. The type of specificity is important in understanding the evolutionary response to natu ral enemies and was studied here in a Drosaphila-parasitoid system. Drosoph ila melanogaster lines selected for increased larval resistance to the endo parasitoid wasps Asobara tabida or Leptopilina boulardi were exposed to att ack by A. tabida, L. boulardi and Leptopilina heterotama at 15 degrees C, 2 0 degrees C, and 25 degrees C. In general, encapsulation ability increased with temperature, with the exception of the lines selected against L. boula rdi, which showed the opposite trend. Lines selected against L, boulardi sh owed large increases in resistance against all three parasitoid species, an d showed similar levels of defense against A. tabida to the lines selected against that parasitoid. In contrast, lines selected against A. tabida show ed a large increase in resistance to A. tabida and generally to L. heteroto ma, but displayed only a small change in their ability to survive attack by L. boulardi. Such asymmetries in correlated responses to selection for inc reased resistance to natural enemies may influence host-parasitoid communit y structure.